1Field of the Invention
The present invention relates generally to reluctance motors and, more specifically, to a miniaturized reluctance motor having at least a portion thereof formed using a MEMS fabrication technique.
2Description of the Related Art
A reluctance motor is an electric motor, in which torque is produced by the tendency of the motor's moveable part to move to a position where the inductance of an excited motor winding is maximized. One feature of a reluctance motor is that the motor's moveable part (e.g., a rotor) does not need a permanent magnet. Instead, the rotor may be made of a magnetic material and constructed to have a cogged shape, with the cogs defining the rotor poles. The motor's stator (i.e., the electromagnetically active portion of the motor's stationary part) also has poles, which are associated with coil windings located around the rotor-containing cavity. Depending on the configuration, each motor winding can define one, two, or even more than two stator poles.
When a current is passed through a winding, each corresponding stator pole becomes excited and attracts the nearest rotor pole. As a result, the rotor poles move towards the excited stator poles, thereby rotating the rotor. If stator poles are excited in a particular sequence, e.g., by properly shaped drive pulses applied to the windings, smooth and continuous rotor rotation can be achieved. More details on the principles of operation and control of reluctance motors can be found, e.g., in a book by T. J. E. Miller, “Switched Reluctance Motors and Their Control,” Clarendon Press, Oxford, 1993, pp. 1-70, the teachings of which are incorporated herein by reference.
Many important applications, such as miniature magnetic disk drives, fluid pumps, and gyroscopes, require miniature motors. MEMS-based motors are particularly attractive for these applications because fabrication of such motors is compatible with fabrication of microelectronic circuits. As a result, a MEMS-based motor and the associated control electronics can advantageously be produced as a single integrated device that is generally more reliable and less expensive than its non-integrated analogue. However, one problem with prior-art MEMS-based motors is that their relatively small size renders lubrication of such motors impractical, which results in relatively high friction and short lifetime.